In general, water purifiers may be classified into ultra filtration (UF) membrane water purifiers and reverse osmosis (RO) membrane water purifiers, depending on a water purifying method carried out thereby.
Among them, the RO membrane water purifier has been known as being superior to other water purifying schemes in terms of removing pollutants.
The RO membrane water purifier may include a filtering unit including a sediment filter that receives raw water from a faucet and removes dust particles, dregs, various suspended bodies, and the like therefrom, through 5-micron fine filters; a pre-carbon filter that removes carcinogens (e.g., trihalomethane (THM)), synthetic detergents, harmful chemicals (e.g., insecticides), residual chlorine components, and the like, by activated carbon adsorption; an RO membrane filter that includes a 0.0001-micron RO membrane, removes heavy metals (e.g., lead and arsenic), sodium, various germs, and the like, and discharges concentrated water through a drain pipe; and a post-carbon filter that removes unpleasant odors, tastes, and colors contained in water having passed through the RO membrane filter.
The UF membrane water purifier uses a UF membrane filter instead of an RO membrane filter. The UF membrane filter is a porous filter having tens to hundreds of nanometer (nm) pores, which removes pollutants in water through numerous fine pores that are distributed on a membrane surface.
As described above, the RO membrane water purifier or the UF membrane water purifier may use four filters. However, the RO membrane water purifier or the UF membrane water purifier may additionally use an antibacterial filter or a functional filter. Moreover, the RO membrane water purifier or the UF membrane water purifier may be used as a combinational filter having functions of a variety of filters. For example, a function of a sediment filter and a function of a pre-carbon filter may be embodied in a single combinational filter.
However, in such a water purifier, a post-carbon filter or the like may be easily polluted by bacteria, and bacteria may flow into a storage tank in water. Therefore, bacteria may proliferate in the storage tank. In addition, external bacteria or microorganisms may pass through purified water stored in the storage tank and proliferate therein, and water scale may be formed on the inner wall of the storage tank.
In order to sterilize bacteria or microorganisms having proliferated in a storage tank, there is proposed a technology that sterilizes a storage tank and a purified water drainage passage by adding separate sterilizing chemicals thereto.
However, this method of supplying sterilizing chemicals may be burdensome and inefficient in terms of sterilization management because a user or a water purifier manager needs to separately perform a sterilizing chemical supply operation. That is, in the case of supplying sterilizing chemicals, a user needs to periodically insert sterilizing chemicals when an automatic injection of sterilizing chemicals is impossible. Also, even in the case that automatic injection of sterilizing chemicals is possible, a user also needs to periodically insert sterilizing chemicals. Therefore, this method is very inconvenient to a user.
Furthermore, in the case of injecting sterilizing chemicals, a concentration of the sterilizing chemicals may be unnecessarily high. In some cases, a user or a manager may inject a large amount of sterilizing chemicals or a small amount of sterilizing chemicals. Therefore, sterilizing chemicals may remain in a water purifier after a cleaning process. Therefore, after the cleaning process, it is necessary to perform a rinsing process several times. If the rinsing process is not adequately performed, the remaining sterilizing chemicals may cause harm to a user' health, and a user may experience unpleasant odors from the sterilizing chemicals.
Moreover, since the water purifier manager needs to perform the sterilizing chemical supply operation, costs for sterilizing the water purifier may be incurred. Thus, the user may feel burdened by service charges.
In particular, the water purifier is not sterilized or cleaned by itself. In most cases, the water purifier is sterilized or cleaned by a service agent. Therefore, it is very inconvenient to a user, and the reliability of the water purifier may be degraded over time.
Conditions in which sterilizing chemicals dissolve or flow out from a tank may also be different depending on a water purifier operation condition (for example, a raw water pressure, a flow rate, or the like). For example, when a flow rate is low, a sterilizing concentration may be relatively high. On the contrary, when a flow rate is high, a sterilizing concentration may be low. Therefore, it is very difficult to control the sterilization. When a concentration of sterilizing chemicals is high, unpleasant odors may be generated.
Since the main sterilizing material used in sterilizing chemicals is OCl—, either having a low pH or a very high pH, a lot of odor may be generated thereby. Also, sterilizing performance is merely 1/70 of that of HOCl. Therefore, a large amount of OCl— sterilizing material as compared to HOCl may be required for sterilizing a tank having the same capacity. As will later be described, sterilizing performance may be significantly degraded as compared to a case of using an electrolyzer to produce a sterilizing material mainly made of HOCl, containing a mixed oxidant (MO).
In order to solve a problem of a water purifier which is sterilized using such sterilizing chemicals, there has been proposed a method of automatically sterilizing a storage tank using an electrolyzer. FIG. 1 illustrates a water treatment apparatus disclosed in Korean Patent Application Publication No. 2009-0128785.
As illustrated in FIG. 1, a conventional water treatment apparatus 10 filters raw water, supplied from a raw water supply unit such as a water main 15, through a water purifying filter 14, stores the filtered water in a storage tank 13, and supplies the filtered water through a dispenser 17 when a user requests the supply of water. In this case, if pollution of purified water stored in the storage tank 13 is detected by a pollution level sensor 13a provided in the storage tank 13, or a predetermined period of time has elapsed, hypochlorous acid may be generated using a chloride supply device 11 and an electrolysis device 12, and be supplied to the storage tank 13. A process of cleaning the storage tank 13, which is disclosed in Korean Patent Application No. 2009-0128785, will be described below in detail.
When it is necessary to clean the storage tank 13 through the pollution level sensor 13a, water stored in the storage tank 13 is completely drained into sewage 16 using an extraction pipe G and the dispenser 17 or through a drain pipe F. Alternatively, most water stored in the storage tank 13 is drained into a low water level or a position near a floor. When the drainage of water stored in the storage tank 13 is completed, a valve Vg or Vf is shut off. In order to supply chlorides, such as NaCl or KCl, from the chloride supply device 11 to the electrolysis device 12, and generate a chloride aqueous solution, raw water (service water) may be supplied through a raw water supply pipe B, without passing through the water purifying filter 14, or purified water filtered by the water purifying filter 14 may be supplied through a raw water supply pipe C disposed at a rear end of the water purifying filter 14. In this case, when the chloride and raw water (service water) or purified water is supplied to the electrolysis device 12 and a sufficient period of time has elapsed to dissolve the chloride, an aqueous solution containing hypochlorous acid is generated through the electrolysis (oxidation-reduction reaction) of the chloride aqueous solution by applying a voltage to electrodes 12a of the electrolysis device 12. The storage tank 13 is fully filled with the generated hypochlorous acid aqueous solution and is maintained during a predetermined period time necessary to sterilize and clean the storage tank 13. After the predetermined period of time has elapsed, the hypochlorous acid aqueous solution is drained from the storage tank 13. In order to remove the hypochlorous acid aqueous solution, water having passed through the water purifying filter 14 is supplied to the storage tank 13 through the purified water supply pipe D up to a level of the storage tank 13 equal to that when full, or service water which has not passed through the water purifying filter 14 is supplied to the storage tank 13 through a rinse pipe H up to a full water level of the storage tank 13. After a predetermined period of time has elapsed, a rinse process of draining rinse water stored in the storage tank 13 is performed several times. In this way, the process of cleaning the storage tank 13 is completed. Then, raw water is filtered through the water purifying filter 14, and purified water is supplied to the storage tank 13, so that a user can use the purified water.
Since the conventional water treatment apparatus is provided with a single storage tank 13, it is easy to sterilize and clean the storage tank. However, since a water treatment apparatus having an ice maker and a plurality of tanks has recently been introduced, there is a need for a sterilizing method that takes into consideration water flow among a plurality of tanks.